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The three components that are required for a fire to start are an ignition source, fuel and a supply of oxygen. Since it is difficult to exclude oxygen from a building, fire prevention tends to concentrate on the other two components.

Human carelessness is the most common cause of ignition and the most difficult to design against. Fires may be started by cigarettes, candles, matches, cooking and other appliances. Deliberate acts of arson are also very difficult to design out.

Buildings must be designed so that occupants can escape safely if a fire breaks out. They must be able to reach a place of safety without being overcome by heat or smoke, and so the time taken to escape needs to be shorter than the likely time it will take for fire or smoke to spread.

This can be achieved by controlling fire spread and by ensuring that escape routes are easily accessible and neither too long nor too complex. People with mobility problems who may need assistance must also be considered.

Escape strategies might include:

Egress: simple direct escape from a building when an alarm is sounded.

This aims to limit the threat posed by a fire to adjoining properties and people outside the building, as well as to limit the possibility of a fire starting as a result of a fire in an adjoining building.

Even when well designed, it is inevitable that doors on escape routes will have to be opened and that smoke will therefore flow into the protected area. This danger can be reduced by using lobbyaccess to staircases which provide a form of 'airlock' where only one door will be open at any time.

An alternative approach is to pressurise protected areas such as corridors and stairs. Fresh air is supplied to the area to be kept smoke-free and the air pressure is maintained above that of surrounding rooms. If a door into the pressurised area is opened, air will flow out rather than smoke flowing in.

The simplest way of stopping smoke spreading within a building is to allow smoke to escape to the outside. This will not extinguish the fire but it will tend to contain smoke to its area of origin and gain time for people to escape and for measures to extinguish the fire to be taken.

Smoke venting systems must be designed to ensure that the smoke being added to the smokelayer is exactly balanced by that being expelled through the vents so that the depth of the smokelayer remains constant and does not descend to a level where it endangers the occupants (2.5m clear height).

In certain buildings, it can be difficult for the fire-and-rescue service to safely reach and work close to fires. Under such circumstances, additional facilities are required to ensure that there is no delay and to provide a secure operating base. This might include: